In general, a thermally sensitive recording medium is prepared by pulverizing a colorless or pale colored basic leuco dye and a color-developing agent to fine particles respectively, mixing these two fine particles with additives such as a binder, a filler, a sensitizer, a slipping agent or others and forming a coating, then coating the obtained coating on a substrate such as paper, synthetic paper or plastics. The prepared thermally sensitive recording medium develops color by an instant chemical reaction by heating with a thermal head, a hot stamp, a thermal pen or laser and a recorded image can be obtained. A thermally sensitive recording medium is widely applied in a facsimile, a printer of computer, a bending machine for a ticket and a recorder of various measuring instruments. Recently, recording equipment has begun to have more diversity and high quality and, along with said tendency, high-speed printing and high-speed formation of images are becoming possible, and an excellent quality for the recording density of a thermally sensitive recording medium is required. Further, along with the diversibility of usage, the performance of a high quality recorded image is required in all regions from a lower density to a high density.
As a method of satisfying the above-mentioned requirements, a method of improving the surface smoothness of a thermally sensitive recording medium by a super calendar is ordinary carried out, however, a printed image of sufficient quality cannot always be obtained. Further, it is well known that the uniform coating of an undercoating layer is necessary for formation of a high-quality printed image, and a method of improving the smoothness of the undercoating layer, for example, using a super calendar is known. Still further, for the purpose of providing a thermally sensitive recording medium which is superior in dot reappearance, for example, a method to accumulate first and second intermediate layers is proposed in patent document 1.
Patent document 1; JP 2000-108518 publication